There is known a wire bonding method in the production process of a semiconductor device having a plurality of semiconductor elements laid one over another on a substrate, which sequentially connects electrode pads of each semiconductor element and lead electrodes of the substrate by wires. In this method, in order to secure bonding strength of the wire to an electrode pad, a bump may be formed on the electrode pad beforehand, and a wire leading from another electrode pad may be bonded to the bump. In addition to the bonding step of passing out wire to bond, the step of making bumps is needed, resulting in the number of steps for wire bonding being increased. In the case of forming bumps beforehand, the process time becomes longer, and also it costs more because the consumption of material increases.
As a method of reducing the number of steps for wire bonding by omitting the formation of bumps on electrode pads, for example, a method is disclosed wherein a fold of wire is formed at the neck portion of a ball bond instead of forming bumps and wherein a wire leading from another electrode pad is bonded to the fold. In the case of performing wire bonding by this method, it is required that enough bonding strength of the wire at the connection can be secured.